Determination of the metastatic status of the primary lymphatic drainage site of melanoma and breast cancer is one of the most important prognostic indicators of survival and probably the single most important determinant of adjuvant treatment. The technique of sentinel node determination was pioneered by Donald Morton for staging of melanoma and has now been extended to the staging of T1-T3 breast cancer patients who present with clinically negative axillary nodes. The biological behavior of metastatic progression from primary site to first, second, and third axillary node levels, with skip metastases found in approximately 2% of cases, has been established. Therefore, determination of the metastatic status of the first drainage node (sentinel node) within the first level of the axillary nodes would be anticipated to define whether a total axillary node dissection were required for staging. Hence the technique of sentinel node detection in the staging of early breast cancer is becoming the standard of care. Sentinel node detection as used in melanoma initially involved the use of blue dyes and quickly extended to the use of blue dyes plus lymphoscintigraphy with Tc-99m labeled sulfur colloid nano-particles or human albumin. The technique as applied to defining the sentinel node in breast cancer is extremely sensitive (approximately 98%) and has the potential for avoidance of axillary node dissection with its attendant acute and chronic complications. Lymphoscintigraphy entails injection, the day before surgery, of the radiolabeled colloid/protein at the borders of the primary tumor or intradermally just above the primary tumor. Three hours after injection, gamma ray detection is used to mark the skin above the sentinel node. The following day, just 30 minutes before surgery, a visible blue dye is injected into or just around the primary tumor. At the time of surgery, a small incision is made at the previously marked site, and a hand-held gamma probe is used to direct the surgeon down to the sentinel node(s). The blue dye confirms the site of the sentinel node. We are developing an alternative method, lymphofluorescentigraphy, to detect sentinel nodes. Lymphofluorescentigraphy is possible because tissue is relatively transparent to electromagnetic light in the near infrared, 750-1000 nm. Consequently an optical window exists in which infrared detection within tissue can be detected and localized. We propose coupling 30-40 nm nanoparticles with a dye that fluoresces in the infrared. The infrared fluorescent nanoparticles will be injected into the immediate area of a primary breast cancer and infrared fluorescence emitted from the sentinel node will be detected from the skin surface. The advantages of lymphofluorescentigraphy are that it should be portable and relatively inexpensive, as well as eliminating the potential danger to patient and medical personnel incurred from radioactive material use and obviates the expense and inconvenience of gamma counting done the day before surgery. Unlike lymphoscintigraphy, lymphofluorescentigraphy will allow the site on the skin just above the sentinel node to be found and marked at the time of surgery. A hand-held fluorescent detection device can be used during dissection to guide the surgeon to the sentinel node(s). Amir Gandjbakliche and colleagues (NICHD) have developed new mathematics to calculate the site of a fluorescent material within tissue. They have shown that the location of a fluorescent phantom placed 3-4 cm into tissue is feasible. Currently, computer assisted devices are being made to find in real time infrared fluorescent materials. Paul Smith, Alec Edsath, and Thomas Pohida are defining, optimizing, and building optical devices and the needed electronics to acquire faint fluorescent signals emanating from tissue. Existing infrared fluorescent dyes are being chemically modified for coupling to albumin or biologically compatible nanoparticles. Animal models have been identified to conduct the initial in vivo studies. The infrared dye containing particles will be injected into the dermis. Thereafter, a detection system will be placed on the skin to define the site of surgical incision, and a hand-held fluorescent detection device will guide the surgeon to the sentinel node.